Most women will experience ovarian hormone loss in their lifetime due to menopause or earlier due to other elective bilateral salpingo-oophorectomy, premature ovarian failure or other causes. Many studies indicate ovarian hormone deficiency is a major risk factor for developing cardiovascular disease (CVD) and CVD is the number one cause of death in women. Conflicting studies over the cardiovascular benefits of hormone replacement therapy (HRT) reflect differing HRT regimens and/or differing subpopulations of postmenopausal women. Thus, a fuller understanding of the biology underlying the effects of ovarian hormone loss and HRT on women?s cardiovascular health is required to comprehensively inform women's decisions regarding the use of HRT especially since HRT is contraindicated in some women. This increased understanding will also facilitate efforts towards developing new therapeutic strategies for women when they reach this point in their lives. Blood vessels are surrounded by perivascular adipose tissue (PVAT), which we and others have shown can modulate vascular function. There is a growing appreciation that adipose tissue has distinct functions depending upon the location of the adipose depot. Thus, we hypothesize that PVAT will exhibit vessel and adipose depot-specific functions. Our research also shows that the vascular protective effects of PVAT on rat mesenteric vessels are lost after ovariectomy; however, it is not known whether this loss in ovarian hormone protection is also observed in other vascular beds and if not, whether differences in ovarian hormone regulation of PVAT function is due to vessel and/or adipose depot-specific effects. Our findings also suggest that restoration of PVAT function could reduce the risk of CVD induced by ovarian hormone loss; however, the HRT conditions under which PVAT function would be protected after ovarian hormone loss remains unclear. Thus, elucidating how ovarian hormone dysfunction and HRT modulates PVAT activity as a function of vascular bed and adipose depot could lead to the development of new PVAT-focused therapeutics for treating vascular dysfunction induced by ovarian hormone loss. These studies led to our overall hypothesis that in order for an HRT regimen in a target population to be cardioprotective, it must preserve the vascular protective effects of PVAT on arterioles in the microcirculation since these resistance vessels play a major role in regulating blood pressure. Aim 1 will determine the role of 17b-estradiol (E2) and follicle stimulating hormone (FSH) in PVAT modulation of mesenteric arteriole vascular reactivity and nitric oxide (NO) and superoxide (O2-) generation. Aim 2 will determine the effect of PVAT modulation of vascular reactivity as a function of the vascular bed and adipose depot. Exploratory Aim 3 will identify biomarkers in circulating peripheral blood mononuclear cells (PBMC) that correlate with altered PVAT function under the experimental conditions. We hypothesize that identified biomarkers will inform clinical trials designed to optimize the composition, timing and duration of HRT regimens. !